In recent years, non-contact power transmission methods for transmitting electric power without passing through a metal contact, connector, or the like have been increasingly used in cordless phones, electric shavers, electric toothbrushes, and the like. In such non-contact power transmission methods, electric power is transmitted by electromagnetic induction between a plurality of coils.
For example, as illustrated in FIG. 9, patent literature 1 (PTL 1) discloses non-contact power transmission equipment in which a secondary coil 102 of a power receiving apparatus 100 is magnetically coupled to a primary coil 101, and the secondary coil 102 is connected in series with a capacitor 103. The power receiving apparatus 100 supplies electric power generated in the secondary coil 102 to a load 107 via a rectifier 104, a filter capacitor 105, and a chopper circuit 106. In this way, in the power receiving apparatus 100, the secondary coil 102 and the capacitor 103 are connected in series and therefore resonate, reducing the reactive power among the electric power generated in the secondary coil 102. Accordingly, the power receiving apparatus 100 can supply electric power to the load 107 while improving the power factor of the electric power.
As illustrated in FIG. 10, patent literature 2 (PTL 2) discloses a power receiving apparatus 200 that includes a secondary coil 202, magnetically coupled to a primary coil 201, and a resonance capacitor 203. The power receiving apparatus 200 further includes a transducer 204 that brings the AC power to a power factor of one by setting parameters of the transducer on the basis of circuit constants measured in advance. The transducer 204 converts the AC power to DC power and supplies the converted DC power to a load 206.